This invention relates to a refractory for use in continuous casting which is placed between a mold and a tundish.
FIG. 1 shows a conventional horizontal type continuous casting apparatus. A feed nozzle 2 is fixed to a lower portion of a tundish 1. The feed nozzle 2 is connected by way of a refractory 3 to a mold 4. The refractory 3 is positioned around an inlet of the mold 4. The molten steel 5 in the tundish 1 is poured through the feed nozzle 2 and the refractoy 3 into the mold 4 where it is cooled thereby to form a solidified shell 6 while it is continuously being drawn.
The refractory 3 must have good thermal shock resistance, wetting resistance with respect to molten steels, corrosion resistance and workability because of required precision in size.
Examples of conventional refractories are a reactive silicon nitride (Si.sub.3 N.sub.4) sintered product and a hot-pressed boron nitride (BN) sintered product. The former has poor thermal shock resistance. The latter has low hardness and poor abrasion.
Other examples of conventional refractories are a Si.sub.3 N.sub.4 sintered product in which BN is contained in Si.sub.3 N.sub.4, a Si.sub.3 N.sub.4 --AlN--BN sintered product in which AlN and BN are contained in Si.sub.3 N.sub.4, and a Si.sub.3 N.sub.4 --AlN--Al.sub.2 O.sub.3 --BN sintered product in which AlN, Al.sub.2 O.sub.3 and BN are contained in Si.sub.3 N.sub.4. The Si.sub.3 N.sub.4 --BN sintered product has good corrosion resistance in casting of carbon steels and poor corrosion resistance in casting of stainless steels. The Si.sub.3 N.sub.4 --AlN--BN sintered products are corroded in casting of carbon steels over a long period as well as in casting of stainless steels. The Si.sub.3 N.sub.4 --AlN--Al.sub.2 O.sub.3 --BN sintered products are corroded in casting of stainless steels a long period of time.